Fitch ratings agency on Friday (May 23) has upgraded Greece's sovereign debt rating, to B from B-, citing the country's improved economic and fiscal outlook.

The New York’s ratings firm cited the country's improved performance under the European Union-International Monetary Fund program, the achievement of a primary surplus - the budget balance excluding interest on outstanding debts, the falling near-term liquidity risk and a better fiscal track record for its upgrade. Fitch kept its outlook on the country at stable.

"Greece achieved a primary surplus in the general government account in 2013, a key target of the EU-IMF programme and an over-performance relative to budget," the New York-based rating company said and described its deficit reduction over the past four years as "remarkable."